U2AF1 and breast cancer: Spliceosomal mutations have also been discovered in a number of solid tumors including breast cancer,27 pancreatic cancer,28 lung cancer,21, 29 and uveal melanoma.19, 22, 30 With the exception of ZRSR2 mutations, somatic mutations in SF3B1, SRSF2, and U2AF1 cause characteristic changes in pre‐mRNA splicing that are distinct from loss‐of‐function, and will be discussed in greater detail in this article.